Great Ormond Street Hospital - UK
This site helps kids learn more about hospitals and illness by reading about the experiences of other kids who have been there themselves. It's also split into sections for different ages of kids.

Polka Theatre - UK/USA
Year 4 kids in the UK and the US work with the Polka Theatre in London to put on plays. Using the web they help each other write and put on the productions, and then watch the plays on the web.

YouthNOISE - USA
Imagine sitting down in a big room and talking to other kids all around the world about any global issue you like. That's the idea behind YouthNOISE, a site that gives kids a chance to voice their opinions on any subject.